The present invention relates to an air suspension, and more particularly to an anti-vacuum system with a separating air spring for a vehicle which requires an axle to be lowered away from the chassis.
A common air suspension system typically comprises bracket secured to a chassis of a vehicle. A longitudinal member extending generally lengthwise of the vehicle is mounted to the bracket for pivoting about an axis generally transverse of the vehicle and to carry an axle having one or more road wheels. An air spring mounted spaced from the axis acts as an adjustable compression spring between the vehicle and the longitudinal member to bias the wheels for effective road engagement and to buffer axle and wheel vibration. The air spring typically includes a piston and an air cell. The piston is mounted to the longitudinal member and the air cell is attached to a bead plate mounted to the chassis.
Vehicles fitted with an air suspension are sometimes used without being inflated such as when being transported on railroad cars. At other times the vehicle axles are left to hang away from the chassis in an unloaded condition on the wheels such as when the vehicle is lifted on and off a ship. These operations cause the air spring to extend without air. Because the air cell is attached to the chassis and the piston is mounted to the longitudinal member, a partial vacuum forms inside the air spring during this expansion. The partial vacuum collapses the air spring air cell inwards and over the top of the piston. When a load is again placed on the suspension the air spring is compressed and the collapsed air cell may become trapped between the piston and upper mounting. Damage to the various rubber parts, connections and mountings can then result when the air spring is reinflated.
Conventional systems to overcome the partial vacuum problem include anti-vacuum valves which allow atmospheric air to enter the air spring if a partial vacuum forms. These systems are only partially effective because the air spring extends faster than air can be drawn through inlet orifices or valving prevalently used.
Other systems allow the air spring to separate from the chassis. The air spring must then be relocated to the chassis when a load is again placed on the suspension. Prior systems provide a cylindrical fitting which receives a post located on the air spring. However, this system creates realignment difficulties as the relatively small fittings can fail to properly relocate the air spring. In addition, a partially inflated air cell is a further impediment to proper air spring realignment as the post is incorrectly positioned for contact with the cylindrical fitting.
Accordingly, it is desirable to provide an improved air suspension for a vehicle which allows the axle assembly to extend away from the chassis and be laterally relocated for consistent reengagement irrespective of the inflated condition of the air cell.